Showing papers on "Monoamine oxidase B published in 1995"

The monoamine oxidase-B inhibitor L-deprenyl protects against 3,4-methylenedioxymethamphetamine-induced lipid peroxidation and long-term serotonergic deficits.

Abstract: 3,4-Methylenedioxymethamphetamine (MDMA)-induced serotonergic neurotoxicity was assessed in the striatum, hippocampus and frontal cortex of rats by using [3H]paroxetine binding to label serotonin (5-HT) uptake sites and 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels as markers of serotonergic function. NMDA (40 mg/kg) induced a significant decrease in both [3H]paroxetine binding Bmax and 5-HT and 5-HIAA levels 7 days after treatment. The monoamine oxidase-B inhibitor L-deprenyl (2 mg/kg) administered 30 min before MDMA blocked these decreases. MDMA (40 mg/kg) also maximally increased the formation of thiobarbituric acid reactive substances (an indicator of lipid peroxidation) 12 hr after treatment in all three brain regions studied. This increase in malondialdehyde formation was also blocked by pretreatment with L-deprenyl. Tryptophan hydroxylase (TPH) activity was also significantly reduced 18 hr after MDMA. L-Deprenyl reversed this decrease in TPH activity. Another experiment confirmed that a significant fraction of [3H]dopamine uptake into hippocampal synaptosomes was blocked by 500 nM fluoxetine, a selective 5-HT uptake inhibitor. These data suggest that the deamination by monoamine oxidase-B of excessive dopamine within the 5-HT terminal generates hydrogen peroxide that may lead to membrane lipid peroxidation, and perhaps other oxidative insults, resulting in selective 5-HT terminal degeneration subsequent to MDMA treatment.

An allelic association study of monoamine oxidase B in Parkinson's disease.

Abstract: A single-stranded conformational polymorphism in the monoamine oxidase B gene was shown to be A or G, 36 bases upstream from the intron 13-exon 14 boundary. An allelic association study revealed no statistically significant associations between this single-base polymorphism and Parkinson's disease, unlike the results of a previous study.

Evidence for a genetic association between alleles of monoamine oxidase a gene and bipolar affective disorder

Abstract: We present evidence of a genetic association between bipolar disorder and alleles at 3 monoamine oxidase A (MAOA) markers, but not with alleles of a monoamine oxidase B (MAOB) polymorphism. The 3 MAOA markers, including one associated with low MAOA activity, show strong allelic association with each other but surprisingly not with MAOB. Our results are significant only for females, though the number of males in our sample is too small to draw any definite conclusions. Our data is consistent with recent reports of reduced MAOA activity in patients with abnormal behavioral phenotypes. The strength of the association is weak, but significant, which suggests that alleles at the MAOA locus contribute to susceptibility to bipolar disorder rather than being a major determinant.

The role of monoamine oxidase and catechol O-methyltransferase in dopaminergic neurotransmission.

Abstract: The action of dopamine (DA) released in the synaptic cleft is mainly terminated by its reuptake and catabolism by the enzymes monoamine oxidase (MAO) and catechol O-methyltransferase (COMT) Preclinical data show that the reduction of the catabolism of DA elicited by MAO and COMT inhibitors leads to an enhancement of DA neurotransmission Moreover, there is evidence suggesting that MAO-B inhibition might protect DA neurons from oxidative stress Nevertheless, due to differences in enzyme localization and activity between man and rodents, results obtained in experimental animals might not reflect the actual situation in humans Today the availability of potent and selective MAO and COMT inhibitors makes it feasible for the clinician to test whether the blockade of catabolic enzymes would result in a symptomatic improvement in Parkinsonian patients, and whether MAO-B inhibition might additionally exert a neuroprotective effect

Phenylethylamine modulation of affect: therapeutic and diagnostic implications.

Abstract: A review of the literature indicates that brain phenylethylamine (PEA) may be a neuromodulator of aminergic synapses and that it promotes energy, elevates mood, and favors aggression. Phenylacetic acid, the main metabolite of PEA, is decreased in the biological fluids of depressed subjects and schizophrenic subjects and is increased in schizoaffective subjects. The administration of PEA or of its precursor L-phenylalanine improves mood in depressed patients treated with a selective monoamine oxidase B inhibitor. The authors speculate that studies of PEA metabolism may have diagnostic value and that PEA administration may be therapeutic in selected depressed patients.

Regions of the Molecule Responsible for Substrate Specificity of Monoamine Oxidase A and B: A Chimeric Enzyme Analysis

Abstract: To examine regions of the monoamine oxidase (MAO, EC 1.4.3.4) molecule responsible for substrate recognition, a series of these enzymes, in which discrete regions in one molecule were substituted by corresponding sequences of the other, were constructed from the cDNAs of rat liver MAO A and MAO B and were expressed in yeast, Saccharomyces cerevisiae. Substrate specificities of the original and chimeric enzymes were examined in terms of the maximum activity (Vmax) and the affinity (Km) for serotonin, beta-phenylethylamine (PEA), and benzylamine. Chimeric enzymes with the amino-terminal portion (about 220 residues) and the amino-terminal and middle portions (about 400 residues) of MAO A and MAO B, respectively, exhibited substantially the same Km values as those of the parent enzymes. Extension of the substitution in the middle portion of a chimeric enzyme to the second half of the amino-terminal portion resulted in conversion of the Km values for serotonin to those of the counterpart. Data on relative Vmax values of the chimeric enzymes for the three substrates revealed that the relative catalytic activities were mainly determined by the presence of the middle portion. We conclude from these observations that the region between about residues 120-220 and about residues 50-400 is responsible for determination of the substrate specificity of MAO A and MAO B, respectively, while the middle portion, of about residues 220-400, may relate to the relative catalytic activity towards substrates.

RS‐45041‐190: a selective, high‐affinity ligand for I2 imidazoline receptors

Abstract: 1. RS-45041-190 (4-chloro-2-(imidazolin-2-yl)isoindoline) showed high affinity for I2 imidazoline receptors labelled by [3H]-idazoxan in rat (pKi = 8.66 +/- 0.09), rabbit (pKi = 9.37 +/- 0.07), dog (pKi = 9.32 +/- 0.18) and baboon kidney (pKi = 8.85 +/- 0.12), but had very low affinity for alpha 2-adrenoceptors in rat cerebral cortex (pKi = 5.7 +/- 0.09). 2. RS-45041-190 showed low affinity for other adrenoceptors, dopamine, 5-hydroxytryptamine, and muscarinic receptors and dihydropyridine binding sites (selectivity ratio > 1000). 3. RS-45041-190 showed moderate potency for the inhibition of monoamine oxidase A in vitro (pIC50 = 6.12), but had much lower potency for monoamine oxidase B (pIC50 = 4.47), neither of which equated with its affinity for I2 receptors. 4. RS-45041-190 (0.001 to 3 mg kg-1, i.v. and 1 ng-50 micrograms i.c.v.) had only small, transient effects on blood pressure and heart rate in anaesthetized rats. In conscious rats, RS-45041-190 had no effect on body core temperature or tail skin temperature (1 mg kg-1, s.c.) or on activity or rotarod performance (10 mg kg-1, i.p.). There were also no effects on barbiturate sleeping time in mice after doses of 1-10 mg kg-1, i.p. 5. RS-45041-190 (10 and 25 mg kg-1, i.p.) significantly increased food consumption in rats for up to 4 h after dosing, but unlike idazoxan (10 mg kg-1, i.p.) did not increase water consumption. RS-45041-190 is therefore a selective, high-affinity ligand at I2 imidazoline receptors and its hyperphagic effect may suggest a role for I2 imidazoline receptors in the modulation of appetite.However, in the absence of a selective agonist it is unclear whether this ligand is an agonist or an antagonist at I2 receptors.

In vivo comparison of the effects of inhibition of MAO-A versus MAO-B on striatal L-DOPA and dopamine metabolism.

Abstract: Utilizing the cerebral microdialysis technique, we have compared in vivo the effects of selective MAO-A, MAO-B, and nonselective MAO inhibitors on striatal extracellular levels of dopamine (DA) and DA metabolites (DOPAC and HVA). The measurements were made in rats both under basal conditions and following L-DOPA administration. Extracellular levels of dopamine were enhanced and DA metabolite levels strongly inhibited both under basal conditions and following L-DOPA administration by pretreatment with the nonselective MAO inhibitor pargyline and the MAO-A selective inhibitors clorgyline and Ro 41-1049. The MAO-B inhibitor deprenyl had no effect on basal DA, HVA, or DOPAC levels. Nervertheless, deprenyl significantly increased DA and decreased DOPAC levels following exogenous L-DOPA administration, a finding compatible with a significant glial metabolism of DA formed from exogenous L-DOPA. We conclude that DA metabolism underbasal conditions is primarily mediated by MAO-A. In contrast, both MAO-A and MAO-B mediate DA formation when L-DOPA is administered exogenously. The efficacy of newer, reversible agents which lack the “cheese effect” such as Ro 41-1049 are comparable to the irreversible MAO-A inhibitor clorgyline. The possible relevance of these findings for the treatment of Parkinson's disease is discussed.

Association analysis of a polymorphism of the monoamine oxidase B gene with Parkinson's disease in a Japanese population.

Abstract: The polymorphic allele of the monoamine oxidase B (MAO-B) gene detected by polymerase chain reaction (PCR) and single-stranded conformation polymorphism (SSCP) was associated with Parkinson's disease (PD) in Caucasians. We characterized this polymorphic allele, allele 1, of the MAO-B gene using direct sequencing of PCR products. A single DNA substitution (G-A), resulting gain of Mae III restriction site was detected in intron 13 of the MAO-B gene. The allele associated with PD in Caucasians was twice as frequent as in healthy Japanese, but the association of the allele of the MAO-B gene was not observed in Japanese patients with PD.

Selective and potent monoamine oxidase type B inhibitors: 2-substituted 5-aryltetrazole derivatives.

Abstract: Twenty new 2-(cyanoalkyl)tetrazoles (15 and 16) and twenty new 2-(hydroxyalkyl)tetrazoles (17 and 18) were synthesized and investigated in vitro for their abilities to inhibit selectively rat brain monoamine oxidase (MAO) B over MAO A. Most of them were MAO B inhibitors and those bearing a substituted 4-(arylmethoxy)phenyl group in the position 5 of the tetrazole ring had IC50 values between 8 microM for 18d and 2 nM for 16a (30 nM for lazabemide) with a selectivity toward MAO B of 37,000 for 16a. The reversibility of their inhibitory activity was demonstrated by in vitro dialysis tests. The 5-[4-(phenylmethoxy)phenyl]-2-(2-cyanoethyl)tetrazole (16a) its derivative 16h and the 5-[4-(phenylmethoxy)phenyl]-2-(2-hydroxyethyl)tetrazole (18a) and its derivative 18h were found to be potent, in vitro selective, and competitive MAO B inhibitors. Tetrazole 16a can be considered one of the most active and selective competitive MAO B inhibitors known up to now. This compound was selected for ex vivo experiments and was shown to be a strong and reversible MAO B inhibitor with a short duration of action after oral administration at 5 mg/kg. The structure-activity approach gives rise to the great importance of lipophilicity over electronic effects of the compounds in these series.

Catecholamine and MHPG plasma levels, platelet MAO activity, and3H-imipramine binding in heroin and cocaine addicts

Abstract: This work evaluated in a population of heroin and heroin plus cocaine human addicts: 1. Norepinephrine (NE), epinephrine (Epi), and 3-methoxy-4-hydroxyphenylglycol (MHPG) (the principal metabolite of brain NE) plasma levels; 2. Monoamine oxidase (MAO) activity; and 3. 3H-imipramine specific binding to the amine carrier in platelets.

Mutagenesis at a highly conserved tyrosine in monoamine oxidase B affects FAD incorporation and catalytic activity.

Abstract: Monoamine oxidase B (MAO B), an integral protein of the outer mitochondrial membrane, catalyzes the oxidative deamination of various neuroactive and vasoactive amines. A covalently bound FAD cofactor at Cys-397 of human MAO B is required for the oxidation of the amine substrates. In addition to the covalent binding site, MAO B also contains a noncovalent FAD binding region (residues 6-34) known as the dinucleotide binding motif. Previously, we have shown that Glu-34 is required for catalytic activity, presumably by forming a hydrogen bond between the carboxylate group of glutamate and the 2'-hydroxyl group of ribose in the AMP moiety of FAD. In this work, we have identified a third FAD binding site in MAO B (residues 39-46) by sequence comparisons to other flavoenzymes. The conserved sequence contains a tyrosine residue (Tyr-44) which, based on the X-ray crystal structure of ferredoxin-NADP+ reductase, is postulated to participate in FAD binding through van der Waals contact with the isoalloxazine ring and a hydrogen bond to the 3'-hydroxy of the ribityl moiety. To test the postulated role of this tyrosine residue, site-directed mutants that encode substitutions at Tyr-44 were prepared and expressed in mammalian COS-7 cells. Variant MAO B enzymes were then characterized with respect to enzymatic activity and [14C]FAD incorporation. Substitution of tyrosine with phenylalanine had no effect on MAO B activity or the level of [14C]FAD incorporation compared to the wild-type enzyme, indicating that the hydroxyl group of the tyrosine residue was not essential at residue 44.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminium cation radical mechanism proposed for monoamine oxidase B catalysis : are there alternatives ?

Abstract: 1. The interaction of bovine liver mitochondrial monoamine oxidase B (MAO B) with a series of benzylamine analogues was investigated to provide mechanistic information relative to the proposed cation radical mechanism and to provide information on the structural requirements of the substrate binding site.2. Steady-state kinetic analysis of MAO B with 11 ring-substituted benzylamine analogues showed substitution does not alter the reaction pathway. All amine analogues tested exhibit sizeable deuterium kinetic isotope effects.3. Anaerobic stopped-flow kinetic studies showed (1) C-H bond cleavage is rate-limiting in enzyme-bound flavin reduction and (2) that no specially detectable flavin radicals are observed.4. The binding affinity of para-substituted benzylamine analogues to MAO B increased as the hydrophobicity of the substituent increased. In contrast, meta-substitution of the ring showed reduced affinity with an increase in the van der Waals volume of the substituent.5. The rate of enzyme reduction by ...

Effects of chronic oral administration of L-deprenyl in the dog.

Abstract: Dogs were administered capsules containing l -deprenyl daily over 3 weeks at dose levels of 0, 0.1, 0.5, and 1.0 mg/kg. Spontaneous behavior was measured using a canine open field test, and was not significantly affected by l -deprenyl. Plasma levels of amphetamine showed a clear dose-dependent elevation 2 h following treatment, but were markedly lower after 24 h, and were undetectable 5 days following the last treatment. Plasma levels of phenylethylamine were increased, but were highly variable. Animals sacrificed 1 day following the last treatment showed a dose-dependent inhibition of monoamine oxidase B in the brain, liver, and kidney, whereas monoamine oxidase A was unaffected in these tissues. l -Deprenyl also caused an increase in phenylethylamine in the striatum and hypothalamus, but not in the neocortex. Brain levels of DA, DOPAC, 3-MT, HVA, 5-HT, and 5-HIAA were unaffected. The pharmacological profile for the dog is distinct from that of other species in that long-term treatment did not produce any significant inhibition of MAO-A activity. The absence of an effect on biogenic amines or metabolites suggests that the metabolism of dopamine is mediated at least in part through pathways other than MAO-B in the normal adult dog.

Inhibition of monoamine oxidases by haloperidol and its metabolites: pharmacological implications for the chemotherapy of schizophrenia

Abstract: The effect of haloperidol and its metabolites on human platelet monoamine oxidase B (MAO-B) and human placenta monoamine oxidase A (MAO-A) in vitro has been investigated We found that 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HP+), 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6- tetrahydropyridine (HTP) and 4-chlorophenyl-1,2,3,6-tetrahydropyridine (CPTP) are potent inhibitors of MAO HP+ appeared to be a reversible, uncompetitive and selective MAO-B inhibitor with a Ki of 083 microM HTP was found to be an irreversible, uncompetitive and selective MAO-B inhibitor (Ki of 184 microM) CPTP inhibits both MAO-A and MAO-B Some other haloperidol metabolites, ie 4-(4-chlorophenyl)-4-hydroxypyridine (CPHP), 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6- tetrahydropyridine N-oxide (HTPNO) and reduced haloperidol (RHAL), do not inhibit MAO to any appreciable degree at concentrations up to 100 microM The results suggest that haloperidol metabolites may contribute to the reduction of platelet MAO-B activity in schizophrenic patients undergoing neuroleptic chemotherapy An examination of the literature reveals that schizophrenic patients with low platelet MAO activity exhibit a strong association with the use of haloperidol Other possible pharmacological implications of the inhibition of MAO activity are discussed

Neurochemical, neuroprotective and neurorescue effects of aliphatic N-methylpropargylamines; new MAO-B inhibitors without amphetamine-like properties.

Abstract: A series of aliphatic N-methylpropargylamine MAO-B inhibitors have been synthesized and their structural and functional relationships have been investigated. 2-Hexyl-N-methylpropargylamine (2-HxMP), for example, has been found to be a highly potent, irreversible, selective, MAO-B inhibitor both in vitro and in vivo. The R-(-)-enantiomers are much more active than the S-(+)-enantiomers at inhibiting MAO-B activity. Some of these compounds protect mouse nigrostriatal dopamine neurons against the neurotoxin MPTP and the mouse hippocampal noradrenergic system against the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). They rescue hippocampal neurons after damage induced by ischemia and kainic acid treatment, as well as motoneurons in young mice following facial nerve axotomy. Such rescue effects are, interestingly, unrelated to inhibition of MAO-B activity. Some of the aliphatic propargylamines enhance the survival of neuroblastoma cells co-cultured with astrocytes following serum depletion. They stimulate the expression of AADC mRNA and inhibit GFAP mRNA expression. They do not possess amphetamine-like properties and exhibit no effect on noradrenaline or dopamine uptake nor do they increase hypertensive effects in the tyramine pressor test. Unlike R(-)-deprenyl, 2-HxMP does not potentiate dopamine toxicity in vitro. These new MAO-B inhibitors may possess significant chemotherapeutic implications for certain psychiatric and neurodegenerative disorders.

Monoamine oxidase-B-positive granular structures in the hippocampus of aged senescence-accelerated mouse (SAMP8)

Abstract: We examined the histochemical localization of monoamine oxidase in the hippocampus of young and old senescence-accelerated mouse (SAM) We found a monoamine oxidase-B-positive granular structure (MGS) in the hippocampus of old SAMP8, an accelerated senescenceprone line of SAM The MGS was a round-shaped granular structure of 05 to 5 μm diameter and usually formed a cluster, the largest diameter of which ranged from 50 to 150 μm No MGS were found in the hippocampus of young SAMP8 or of young SAMR1, an accelerated senescence resistant line of SAM, and only few, if any, were seen in old SAMR1 A monoamine oxidase-positive astrocyte was usually observed in the central area of each cluster of MGS Furthermore, the MGS was in close anatomical relationship with monoamine oxidase-positive astrocytic processes The enzyme inhibition experiments showed that monoamine oxidase activities localized in the MGS and astrocytes were both predominantly of type B These findings suggest MGS occurs at least partly in monoamine oxidase-B-positive astrocytes Furthermore, the MGS was similar to a periodic acid-Schiff-positive granular structure, a polyglucosan body previously documented in the brains of old SAMP8 and some other aged mice strains including C57BL/6 and nude mice, in terms of their size, morphological appearances and topographical distribution in the hippocampus Thus, the present results suggest that monoamine oxidase type B is a proteinaceous component of the periodic acid-Schiff-positive granular structure in aged mice brains, and might provide some clues for clarifying the mechanisms of age-related occurrence of periodic acid-Schiff-positive granular structures in mice brains

Selegiline induces "trophic-like" rescue of dying neurons without MAO inhibition.

Abstract: Selegiline has been claimed to slow the progression of motor deficits in Parkinson’s Disease (PD)1 and cognitive decline in Alzheimer’s Disease (AD)2 It is controversial whether the slowing represents a symptomatic action due to improved dopaminergic neurotransmission or neuroprotection due to a decrease in the production of toxic oxidative radicals consequent on the inhibition of monoamine oxidase B (MAO-B) We propose a third action for selegiline — a “trophic-like” rescue of dying neurons

Specification of the phenotype required for men with monoamine oxidase type A deficiency

Abstract: Brunner et al. (1993 a, b) reported on a Dutch family, in which complete monoamine oxidase type A (MAO-A) deficiency due to a point mutation in the respective gene is associated with a \"recognizable behavioral phenotype\" (all quotations refer to Brunner et al. 1993 a, b) that includes distrubed regulation of impulsive aggression. Understandably, these findings received considerable coverage in both the scientific (Morell 1993) and lay press, because for the first time aggressive behavior had been linked to a single gene mutation. However, in our opinion the clinical delineation of the phenotype appears so vague that it can be questionned whether it indeed results from the mutation. Our criticism specifically pertains to (1) inadequate delineation of the cognitive and behavioral phenotype, (2) the assumed X-linked inheritance of the phenotype and (3) the lod score calculation, which was performed without assuming a phenocopy rate.